Process of concentrating solutions of synthetic linear polyamides



Patented Nov. 29, 1949 PROCESS OF CONCENTRATING SOLUTION OF. SYNTHETICLINEAR POLYAMIDES Robinson Percy Foulds andwilliam Hilton Roscce,Manchester, England,

Company Limited, Manchester,

Broadhurst Lee England No Drawing.

No. 782,024. In

assignors to Tootal Application October 24, 1947, Serial GreatnrltainNovember 1, 19.40

8 Claims- (CL 26030.8)

The present invention relates to improvements in the preparation ofsolutions or dispersions synthetic linear polyamides including polyamidelnterpolymers especially linear superpolyamides;

In United States patent application Serial No. 524,105, R. P. Foulds,filed February 26, 1944, now abandoned, and in continuation applicationSerial No. 764,575, R. P. Foulds, filed July 29, 1947,- there isdescribed a process of treating fibrous material which consists inapplying to it a liquid solution of water insoluble synthetic linearpolyamide in strong acid and then precipitating the polyamide on saidmaterial by an aqueous medium which is substantially non-solvent forsaid polyamide.

' Synthetic linear polyamides are known in commerce as "nylon and areorganic condensation products which contain a multiplicity of structuralunits linked in series by amide or thio amide groupings, produced by aprocess of manuiacture in which non-fiber-forming organic substances oflower molecular weight are converted into products of such highmolecular weight as to be capable of being formed into filaments whichupon cold drawing acquire a true fiber structure recognisable by X-rayexamination. When used in reference to textile art, the term nylon" isnot customarily applied to synthetic polyamides which are water-soluble.The present invention is concerned with water-insoluble, high molecularweight or fiber-forming polyamides soluble in strong acid such as aredescribed in United States patent specification No. 2,071,250, WallaceH. Carothers, patented February 16, 1937; United States patentspecification No. 2,071,253, Wallace H. Carothers, patented February 16,l93'l,-. and United States patent specification No. 2,130,948, WallaceH. Carothers, patented September 20,

It will be apparent therefore, that many of these synthetic linearpolyamides are made from alkylene diamines and higher aliphaticdlcarboxylic acids. Examples of these are polyalkylenediamine adipatesand polyalkylenediamine sebacates.

For many purposes and in particular for the purpose of carrying out theprocess described in the aforesaid patent application Serial Nos. 524,-105 and 764,575, it is useful to have solutions of synthetic linearpolyamides in mineral acids in which the proportion of polyamide ishigh. Some difficulty is encountered in making such solutions owing tothe slowness with which the polyamides dissolve in mineral acids alreadycontaining substantial amounts of polyamides in solu- 2 tion. Moreover,as is well known, synthetic linear polyamides are hydrolysed by mineralacids. Al-j though the rate of hydrolysis is slow enough to enable suchsolutions to be made and used, the

polyamide does become degraded'when the solutions are allowed to standfor any lengthy period e. g. over one or two days.

One object of the present invention is to provide solutions containinghigh proportions of synthetic linear polyamides in .mineral acids.Another object is to concentrate solutions of poly amides in mineralacids thereby to obtain solutions containing a higher proportion ofpolyamide than can conveniently be produced by direct dissolution'of thepolyamides in acids. Another object is to produce solutions of highviscosity containing synthetic linear polyamides in mineral acids.Another object is to produce solutions of synthetic linear polyamides inacids which only' degrade slowly on standing. Another object is toproduce solutions of synthetic linear polyamides in sulphuric acid whichcan be kept for several days at atmospheric temperature without seriousdegradation.

It has been found that if a solution is first made by dissolving asynthetic linear-polyamide, or two or more different synthetic linearpolyamides, in hydrochloric, sulphuric, nitric or phosphoric acid and inthis solution is dissolved sufficient of a salt of hydrochloric,sulphuric, nitric or phosphoric acid which is soluble in the acid inwhich the polyamide is dissolved, then the solution separates into twolayers, one consisting substantially of acid and salt and contain-. ingvery little polyamide and the other substantially of a. solution of thepolyamide in acid and containing very little salt. The two layers may beseparated from one another in any convenient manner to enable each to beisolated. The last mentioned layer contains a very high proportion ofsynthetic linear polyamide and can be used for whatever purpose a highlyconcentrated solution of such polyamide in acid is required.

As will be appreciated, solutions of synthetic linear polyamides inmineral acids may not in all cases be true solutions but have many ofthe characteristics of dispersions owing to the high molecular weight ofthe polyamides. particularly true of the solutions containing high.

proportions of polyamides. Nevertheless the liquid solutions appearhomogeneous and do not exhibit any settling of the polyamide so that,

for convenience, we shall herein refer to solu-{ tions whatever theconcentration may be.

This is,

.in most cases giving aseaseo A solution of polyamide in one of the fourmineral acids named above does not separate into two layers until acertain minimum amount of the salt has been dissolved The mini, mumamount required depends upon the nature of the polyamide, the nature ofthe acid, the quantity of water in the acid, the concentration of thepolyamide in the acid, the nature of the salt and the temperatureemployed. It is found in some cases that some salts may beinsuiiiciently soluble to bring about separation into two layers, anexample of this being aluminium sulphate in the case of a solution madeby dissolving the synthetic linear polyamide obtained from hexamethylenediamine and adipic acid in aqueous 45% by weight sulphuric acid. In theexamples hereinafter given. all of which are carried out at roomtemperature, the amount of salt employed is approximately the minimumwhich will cause separation into two layers. Larger quantities areunnecessary but can be employed rise to a higher concentrain the layercontaining the this. However, in some cases it is possible for thesolution to dissolve so much of the salt that the layer containing thelarger proportion of polyamide is not homogeneous and may even show agel formation: this is usually undesirable.

'Ihesaltusedmustbesuchthatitwillnotreact undesirably with the acid oracids in which the polyamide has been dissolved. We have found itconvenient. although not always essential, to use a salt of the acidactually used to dissolve the polyamide, for example sodium sulphate inthe case where sulphuric acid has been used as the acid solvent. Thesalt may be for example the salt of an alkali metal, of ammonium, of analkaline earth metal, or of zinc, or of magnesium. Mixtures of salts ormixed salts may be used.

By the present invention, it is possible to make solutions of syntheticlinear polyamides in hydrochloric, sulphuric, nitric or phosphoric acideonhigh proportions of polyamide more easily than by directly dissolvingsuch high proportion of polyamide in such acid. Indeed, we have not beenable to prepare, by directly dissolving the polyamide in the acid, someof the highly concentrated solutions obtainable by the process of thepresent invention and these highly concentrated solutions are believedto be novel. Thus, the invention enables solutions of synthetic linearpolyamides to be made in sulphuric acid, for example aqueous 45% byweight sulphin-icacid, containing more than 20 grams of polyamide andeven more than 25 grams of polyamide per 100 cc. of liquoras well assolutions t synthetic linear polyamides in hpdrochloric acid, forexample aqueous 20% by weight hydrochloric tion of polyamide largerproportion of acid, containing more than 25 grams of polyamide per 100c.c. of liquor and solutions of synthetic linear polyamides in nitricacid for example aqueous 63% by weight nitric acid, containing more than25 grams of polyamide per 100 c.c. of liquor. .c

The solutions of synthetic linear polyamides in mineral acids preparedby the present invention show less tendency to degradation thansolutions made by directly dissolving the polyamide in the mineral acid.Accordingly. they can be kept for longer times without the film formingproperties of the polyamide being destroyed. Indeed in most cases theconcentrated solutions obtained by the invention show less tendency todegradation than the solutions of lower polyamide content from whichthey were made.

Fibrous or other materials may be treated with solutions of syntheticlinear polyamides in hydrochloric, sulphuric, nitric or phosphoric acidconcentrated by the process of the present invention. paper or textilematerials may be I For example, treated with the dispersion and thenpassed through an aqueous medium such as water to deposit the polyamidefrom the dispersion on to the paper or fabric as a filler or coating.The polyamide may be precipitated locally to produce pattern effects.

These solutions of synthetic linear polyamides made by the presentinvention are not only of a comparatively high concentration but arealso of a comparativelyhigh viscosity and as a result of this, when theyare applied to a porous material, such as a textile fabric, they tend toremain very largely on the surface of the fabric. This enables glazedeflects on fabrics to be obtained by precipitation of the syntheticlinear ployamide more easily than from less viscous solutions which areabsorbed by the fabric. By the use of these viscous solutions a glazedeil'ect can be obtained merely by precipitating, neutralizing and dryingbut this eflect can be enhanced by calendering. When dyed effects are tobe produced or coloured pattern eflects are to be produced by printing adyestui! on selected areas of the fabric, it may be preferable that thedyestuil' should be applied after the polyamide has been precipitated onto the fabric.

Threads or films may be made by coagulation of solutions concentrated bythe process of the present invention, with an aqueous medium or anaqueous alkaline medium or an alkaline medi illustrated by but is um.The invention will be not limitedto the following examples.

Example 1 5 of the synthetic linear polyamide obtained fromhexamethylene diamine and adipic acid by the method described in Britishpatent specification No. 474,999 and having a melting point of about 248C. were dissolved in 100 c.c. of aqueous by weight sulphuric acid.

The volume of the solution obtained was substantially greater than c.c.so that the concentration of polyamide was less than 5 grams per 100c.c. 7 grams of sodium chloride were dissolved in this solution whichthereupon divided into two layers. The upper layer comprised 19.4 c.c.of a solution of containing 20.2 grams per 100 c.c. of the polyamide andvery little dissolved salt. The lower layer comprised 87.3 c.c. of aclear liquor containing substantially all the salt and only 1.02 gramsof polyamide.

Example 2 The procedure was as in Example 1 except that the initialsolution was made by dissolving 10 grams of the stated polyamide in 100c.c. of aqueous 45% by weight sulphuric acid. After solution of thesodium chloride and separation into two layers the upper layer comprised42.7 c.c. of a solution of polyamide containing 21.3 grams per 100 c.c.of the polyamide and very little dissolved salt. The lower layercomprised 68.1 c.c. of a clear liquor containing substantially all thesalt and only 0.7 gram of polyamide.

Example 3 The procedure was as in Example 2 except that contained lessthan 7.54 grams of sodium sulphate (anhydrous) were used instead of 7grams ofsodium chloride. The upper layer comprised 56 c.c. of a solutioncontaining 9.50 grams of polyamide (17.0 grams per 100 c.c.) and 2.02granis'of sodium sulphate and the lower layer comprised 57 c.c. of aclear liquor containing 5.25 grams of sodium sulphate and 0.3 gram ofpolyamide. There was an inevitable slight loss of material in separatingthe layers.

trample 4 Example 5 The procedure was as in Example 4 but using 19.5grams of zinc sulphate (heptahydrate) instead of 9.5 grams of sodiumsulphate. After separation into two layers. the upper'layer contained26.3- grams of polyamide per 100 c.c.

' Example 6 Example 8 The procedure was as in Example 4 but using 6.5grams of sodium chloride instead of 9.5 grams of sodium sulphate. Afterseparation into two layers, the upper layer contained 26.9 grams ofpolyamide per 100 c.c.

Example 9 The procedure was as in Example 4 but using 10 gramsofammonium sulphate and 1 gram of sodium sulphat'e (anhydrous), instead of9.5 grams of sulphate. A similar result was, obtained as in Example 8.

Example 10 grams of the, synthetic linear polyamide referred to inExample 1 were dissolved in 100 c.c. of aqueous by weight sulphuricacid. The resulting solution contained 28.6 grams of polyamide per 100c.c. 8 grams of sodium sulphate (anhydrous) were dissolved in thissolution which thereupon separated into two layers. The upper layercontained 32.0 grams oi polyamide per 100 c.c. but was not homogeneous.

Example 11 20 grams of the synthetic linear polyamide re- (erred to inExample 1 were dissolved in 100 c.c. of aqueous 20% by weighthydrochloric acid 6.5 grams of zinc chloride were dissolved in thesolution which thereupon separated into two layers of which the lowerlayer contained the greater sulphate (heptahy- 6 part of the polyamidewith very little salt in solution, while the upper layer was a clearliquor containing most of the salt and a very small proportion of thepolyamide. Addition of a larger amount. of zinc chloride caused thelower layer to gel.

Example 12 The procedure was as in Example 11 but using 3.75 grams ofsodium chloride instead of 6.5 grams of zinc chloride. After separationinto two layers, of polyamide per 100 c.c.

Example 13 The procedure was as in Example 11 but using 2.75 grams ofammonium chloride instead of 6.5 grams of zinc chloride. Afterseparation into two layers, the lower layer contained 24.6 grams ofpolyamide per 100 c.c.

Example 14 The procedure was as in Example 11 but using 7.0 grams ofmagnesium chloride (hexahydratelinstead of 6.5 grams of zinc chloride.After separation into two layers, the lower layer contained 25.5 gramsof polyamide per 100 c.c.

Estample 15 20 grams of the synthetic linear polyamide referred to inExample 1 were dissolved in 100 c. c. of aqueous 63% by weight nitricacid. on adding sodium nitrate to the solution, insuilicient woulddissolve to bring about separation into two layers. It was found,however, that on dissolving 17 grams of potassium nitrate in thesolution. this separated into two layers of which the upper layer 71 c.c. contained the greater part of the polyamide with very little salt insolution, while the lower layer (56 c. c.) was a clear liquor containingmost of the salt and a very small proportion of the polyamide. Theamount of polyamide in the upper layer was 27.1 grams per 100 c. c.

Example 16 The procedure was as in Example 15 but using 15.0 grams ofammonium nitrate instead of 17.0 grams of potassium nitrate. Afterseparation into two layers, the upper layer c. 0) con-. tained 24.0grams of polyamide per 100 c. c. while the lower layer (51 c. c)contained very little polyamide.

When an attempt was made to replace the ammonium nitrate with ammoniumchloride, some reaction seemed to occur and nitric oxide was evolved.

Example 17 10 grams of the synthetic linear polyamide referred to inExample 1 were dissolved in 100 c. c. of aqueous orthophosphoric acid byweight HaPOO The polyamide dissolved very slowly and dissolution tookabout five hours. 23 grams of trisodium phosphate were dissolved in thesolution which thereupon separated into two layers of which the upperlayer (51 c. c) contained the greater part of the polyamide (19.6 gramsper c. c.) with very little salt in solution, while the lower layer('7'! c. c.) was a clear liquor containing most of the salt and a verysmall proportion of the polyamide.

Example 18 6 grams of the synthetic linear polyamide referred to inExample 1 were dissolved in 100 c. c. of aqueous orthophosphoric acid(90% by weight the lower layer contained 26.0 grams v upper layer (30 c.c) contained the greater part of the polyamide (20.0 grams per 100 c.c.) with very little salt in solution, while the lower layer (110 c. c.)was-a clear liquor containing most of the salt and a very smallproportion of the polyamide.

Sodium chloride was found to be insufliciently soluble in the solutionto bring about separation into two layers.

Example 19 grams of the synthetic linear polyamide ob tained fromhexamethylene diammonium adipate and aminostearic acid by the methoddescribed in British patent specification No. 559,514 and having amelting range of 135-160 C. were dissolved in 100 c. c. of aqueous 45%by weight sulphuric acid, 5.5 grams of sodium chloride were dissolved inthe solution which thereupon separated into two layers of which theupper layer- (68.5 c. 0.) contained the greater part of the polyamide(27.8 grams per 100 c. c.) with very little salt in solution. while thelower layer (33.6 c. c.) was a clear liquor containing most of the saltand a very small proportion of the polyamide (0.18 gram).

The invention is not limited to the preparation of solutions .of thepolyamides'employed in the above examples. Solutions of other polyamidesmay be made by the process of the present invention which may, indeed,be applied to any synthetic linear polyamide which is soluble inhydrochloric, sulphuric, nitric or phosphoric acid.

For example, the polyamide obtained from ethylene diamine and sebacicacid having a melting point of about 254 C. (see United States patentspecification No. 213,948) or the polyamide obtained fromtetramethylenediamine and adlpic acid having a melting point of about278 C. (see British patent specification No. 474,999) or the polyamideobtained from paraxylylenediamine and sebacic acid and havin a meltingpoint of about 268 C. or the polyamide obtained frompentamethylenediamine and brassylic acid and having a melting point ofabout 176 C. (see United States patent specification No. 2,130,948) maybe used.

It is known that synthetic linear polyamides are degraded by strongacids. Although solutions in hydrochloric, sulphuric, nitric orphosphoric acid can be made which show little or not degradation whenfresh, degradation takes place on standing. It is one of the importantadvantages of the present invention that solutions of polyamidesprepared by the process of the invention give more permanent eflectswhen used for treating materials than solutions of the same strengthmade by directly dissolving the polyamide in the mineral acid, when bothhave been kept for some time due to less degradation of the polyamide.This can readily be tested. Two methods are available.

1. A thin coating of the two comparative mineral acid solutions isspread on a glass plate and treated with water to precipitate thepolyamide. The polyamide precipitates from the solutions made accordingto the present invention adheres strongly and eventually washes oil as afilm whereas the polyamide precipitated from direct acid solution washesoff more easily and in powdery form.

2. A thin coating of the two comparative mineral acid solutions isspread on samples of a light weight cotton fabric. The samples are then8 treated with water to precipitate the polyamide and then washed withsodium carbonate solution and with water to neutralise all the acid.They are then hot pressed and subjected to washing and rubbing. Thepolyamide precipitated from, the solutions made according to the presentinvention show much greater adherence, resisting rubbing and washingbetter than polyamide precipitated from direct acid solution.

For example, the solution of polyamide employed in Example 4 containing16.7 grams 'of polyamide per c. c. as well as the product of thatexample containing 25.9 grams of polyamide per 100 c. c. gave excellentcoverings when precipitated on cotton fabrics by means of waterimmediately after making and when hot pressed. These coverings adheredstrongly, resisting washingand rubbing.

When cotton fabrics were treated with the same solutions which had stoodfor 6 days, the polyamide precipitated from the second mentionedsolution was more resistant to removal by washing and rubbing than thepolyamide precipitated from the first mentioned solution. The productsof Examples 5, 6, 'l'and 8 behaved similarly to the second mentionedsolution.

The solutions obtained from Examples 11 to 14 showed similar improvementas compared with direct acid solutions but'the improvement of thesolutions obtained from Examples 15 and 16 was most striking sincenitric acid is extremely active in degrading polyamides.

For example the product obtained by Examples 15 and 16 even afterstanding for 3 days gave a covering on the cotton fabric which was moreresistant to removal by washing and rubbing than the covering on thecotton fabric obtained from a solution of 20 grams of polyamide in 100c. c. of aqueous 63% nitric acid after standing only two ays.

We declare that what we claim is:

1.'The process of concentrating a solution of synthetic linear polyamidemade from alkylene diamine and an aliphatic dicarboxyiic acid, in acidselected from the group which consists of hydrochloric acid, sulphuricacid, nitric acid and phosphoric acid which comprises dissolving in saidsolution sumclent of a salt of an acid selected from the said group tocause the solution to separate into two layers one of which contains ahigher concentration of said synthetic linear polyamide than the otherand isolating the layer containing a higher concentration of saidsynthetic linear polyamide.

2. The process as claimed in claim 1 wherein the salt is a salt of theacid in which the said synthetic linear polyamide is dissolved.

3. The process of concentrating a. solution of synthetic linearpolyamide made from alkylene diamine and an aliphatic dicarboxylic acid,in acid selected from the group which consists of hydrochloric acid.sulphuric acid, nitric acid and phosphoric acid which comprisesdissolving in said solution sufilcient sodium chloride to cause thesolution to separate into two layers one of which contains a higherconcentration of said synthetic linear polyamide than the other andisolating the layer containing a higher concentration of said syntheticlinear polyamide.

7o 4. The process of concentrating a solution of synthetic linearpolyamide made from alkylene diamine and an aliphatic dlcarboxylic acid,in acid selected from the group which consists of hydrochloric acid,sulphuric acid, nitric acid and 15 phosphoric acid which comprisesdissolving in said solution suflicient sodium sulphate to cause thesolution to separate into two layers one of which contains a higherconcentration of said synthetic linear polyamide than the other andisolating the layer containing a higher concentration of said syntheticlinear polyamide.

5. The process of making a solution of synthetic linear polyamidc madefrom alkylene diamine and an aliphatic dicarboxylic acid which comprisesdissolving said synthetic linear polyamide in sulphuric acid in therelative proportions of to 20 grams of said synthetic linear polyamideto each 100 c. c. of sulphuric acid, dissolving in the soluticn sodiumchloride in the proportion of at least 7 grams for each 100 c. c. ofsulphuric acid to cause separation of the solution into two layers oneof which contains a higher concentration of said synthetic linearpolyamide than the other and isolating the layer containing a higherconcentration of said synthetic linear polyamide.

6. The process of making a solution of synthetic linear polyamide madefrom alkylene diamine and an aliphatic dicarhoxylic acid which comprisesdissolving said synthetic linear polyamide in sulphuric acid in therelative proportions of 5 to 20 grams 01 said synthetic linear polyamideto each 100- c. c. of sulphuric acid, dissolving in the solution sodiumsulphate in the proportion of at least 9.5 grams for each 100 c. c. ofsulphuric acid to cause separation of the solution into two layers oneof which contains a higher concentration of said synthetic linearpolyamide than the other and isolating the layer containing a higherconcentration of said synthetic linear polyamide.

7. The process as claimed in claim 5 in which the strength of thesulphuric acid is substantially by weight. w

8. The process as claimed in claim 6 in which the strength of thesulphuric acid is substantially 45% by weight.

ROBINSON PERCY FOULDS. WILLIAM HILTON ROSCOE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,141,169 Catlin Dec. 27, 19382,342,387 Catlin Feb. 22, 1944 2,388,278 Moncriefl et a1. Nov. 6, 1945

